Footwear such as shoes, boots, ice and roller skates and the like are commonly fabricated by employing a method referred to in the shoe industry as “lasting.” The process is referred to as lasting because the article of footwear is formed over a “last,” which is a three-dimensional rigid shape (e.g., formed of wood or metal) of the inner cavity of the desired form of the footwear. Typically, a mid-sole is first secured to the bottom of the last. Then, various and often numerous component layers of textiles, leather, and/or synthetic materials are glued and/or stitched to one another, stretched over the last and the lower ends folded underneath and secured to the mid-sole to form the “upper” portion of the footwear. Once the components of the upper are assembled to conform with the last, an out-sole is secured to the bottom of the mid-sole over the folded ends of the upper via an appropriate mechanical and/or adhesive means such as stitching, tacks, or glue. An insole or foot bed, often formed of a cushioning material, is then placed within the internal cavity of the footwear over the mid-sole. Additional strength or definition to the footwear may be imparted by incorporation of one or more rigid components in selected areas. The shape of the last not only corresponds to the shape of the inner cavity of the desired form of the footwear but also corresponds to the shape of the foot of the intended wearer. Thus, as a general proposition both the last and the inner cavity of the article of footwear will have regions that are configured to correspond to the toe, heel and mid-regions of the intended foot for which the article of footwear is configured.
Measurement devices such as the “Brannock Device” facilitate sizing the wearer's foot to the appropriate article of footwear. Such measurement devices typically are adapted to taking a heel to toe measurement, a heel to the ball of the foot measurement, and a horizontal/lateral width measurement between the medial and lateral extent of the forefoot and correlating those measurements with standardized footwear sizing schemes.
Performance characteristics of the footwear, such as fit, support, rigidity, flexibility, durability, bulk, weight, protection, and appearance are derived by virtue of the external configuration of the last together with the choice of the construction material employed for a given component, the geometry of each component, the position of the individual components relative to one another and the last, and the manner by which the various components are attached or otherwise secured to one another and stretched over the last. Incremental and selective modification of the individual assembly components and the manner by which they are joined provides the manufacturer significant design and construction freedom. As a result, the lasting process continues to be widely employed and is generally accepted as producing a good quality product by which other footwear products are measured.
The lasting process, however, is time and labor intensive. Moreover, the quality and consistency of lasted footwear is inherently subject to the skill of the particular craftsman and variations inherent in the chosen component materials employed. Consequently, manufacturers have often implemented stringent quality assurance measures, which result in additional cost to an already expensive process. Notwithstanding such measures, it is not infrequent for manufacturers to incur substantial costs due to reworking, scrapping, or sale of the footwear as factory seconds or specials at a reduced price. Nor can such quality assurance measures necessarily avoid the inherent dimensional inconsistency that is endemic to the lasting process; such that seemingly identical footwear having the same manufactured size, nevertheless fit or feel noticeably different. Thus, even with stringent quality assurance measures in place, it is not uncommon for end-consumers to try on several of the same shoe of the same “size” to find a best fitting pair. This is so because once the last is removed from the footwear, the internal cavity of the article of footwear takes on its natural unstressed form and the functional properties resultant therefrom. Hence, slight variations in the manner by which the component elements are stretched or otherwise formed over the last or in the properties or dimensions of the component elements, their interposition, alignment, and/or attachment points may effect both the natural cavity size and the functionality (e.g., flexibility, support, and fit) of the article of footwear.
Furthermore, lasted footwear products, like baseball gloves, often require significant break-in time in order to provide the desired flexibility and fit. This is especially true in the case of ice skates and the like in that those types of footwear are often formed more stiffly by employment of additional, thicker, or stiffer layers of textile or other materials to provide greater support and more efficient transfer of force. It is not uncommon for ice skaters, for example, to have to wear an ice skate for many months to break-in the ice skate. Once broken-in, continued use of the ice skate, however, may often result in the ice skate being physically degraded to the point where it no longer provides the needed support or stiffness in the desired areas, such as at or about regions configured to surround the ankle and the outward protrusions created by the lateral and medial malleolus bone formations. As a consequence, a new ice skate needs to be purchased, which requires yet another break-in period. Moreover, the employment of additional layers of textile materials to fortify the walls of the article of footwear often adds significant weight and bulk. Hence, ice skate boots, for example, typically weigh two or three times that of a dress or street boot of the same size. Furthermore, because optimum performance is achieved between the period of break-in and degradation, performance is transient with time and use.
In an effort to improve upon the lasting process, attempts have been made toward reducing the number of assembly components by employing unitary shell structures made from injected molded plastics. Such shell structures are manufactured typically by preparing a metal mold of the desired internal and external configuration of the shell walls, injecting heated thermoplastics in the liquid stage into the mold, and then cooling the mold to allow the injected thermoplastic to harden. Once hardened, the shell is removed from the mold and employed as either internal or external support to the article of footwear.
Employment of such unitary plastic shell structures may facilitate both control over the end-shape and volume of the footwear as well as utilization of less complicated assembly procedures and techniques. Less skilled labor or in some cases even an automated assembly process is capable of being employed. In addition, the management costs associated with procuring and processing the numerous assembly components in a timely fashion may be commensurately reduced, thereby potentially increasing profit margins. Moreover, such shell structures being formed as a single molded unitary component are capable of providing efficient communication between regions of the footwear that are formed thereby. Thus, reductions in bulk and weight are capable.
Even so, prior art unitary molded plastic shell constructions have their shortcomings. In a lasted footwear product, the walls that form the foot cavity are constructed or otherwise defined by the various and numerous assembly components, each of which having unique functions and properties that are resultant from their shape, material composition, interposition, and the manner and location by which each component is attached to the other. The various material properties of the individual components independently and in conjunction with the other components, thus, define the functionality or performance of the footwear article.
In contrast, injected molded plastic shells are generally isotropic constructs in that they are formed of generally homogenous materials that, at any given location, tend to exhibit homogenous physical properties in all directions following the molding process. Thus, for example, the elastic modulus, which is an indicator of the material's inherent stiffness or rigidity, is generally not dependent on direction, rather it is the same regardless of the direction that the stress is applied.
Engineering unitary injected molded plastic shell structures, therefore, is primarily limited to (1) the choice of plastic material(s), (2) the design of the external and internal configuration of the shell, and (3) the manipulation of the thickness of the chosen plastic material at any given location in the shell. As a consequence, the more substantial the shell component, the more difficult it is to design and the less likely it will provide the wearer with the desired performance. On the other hand, employment of a less substantial shell component tends to negate both the shell's ability to define end-shape and foot cavity volume as well as the likelihood of realizing significant manufacturing efficiencies relative to the lasting process.
To make matters worse, experience has shown that many consumers find such injected molded plastic shell structures to be aesthetically displeasing or otherwise indicative of poor craftsmanship. Consequently, such articles of footwear are subject to the additional expense associated with concealing the plastic shell within more aesthetically pleasing textile materials.
Moreover, because such plastic shell structures are rigidly formed to provide a defined end-shape and foot cavity volume while also providing firm support to the foot, such shell structures have an inherent disadvantage in facilitating flexibility vis-à-vis lasted footwear, which are generally formed of layers of pliable components. Recent attempts to facilitate flex in an otherwise rigid plastic construction have, therefore, tended to use softer plastics (lesser elastic modulus) or more thinly formed plastics molded into selected regions of the shell on the theory that those regions would be more complaisant or amenable to flexing when stressed.
Although, there has been numerous and continuing attempts to design and implement injected molded plastic shell structures to form non-lasted articles of footwear, such attempts have generally not sufficiently overcome the significant aforementioned design hurdles and as a result have been met with limited consumer acceptance. For instance, over the last 25 years or more, non-lasted ice skates employing unitary injected molded plastic shells have repeatedly been introduced to recreational and professional consumers. Nevertheless, most if not all professional hockey players in the National Hockey League (NHL™) continue to skate on nothing other than a lasted ice skate formed of traditional footwear materials or contemporary synthetic substitutes thereof.
There continues, therefore, to be a long felt need in the industry for a footwear construction employing a unitary molded support structure that is capable of one or more of the following: (1) effectuating a controlled end-shape and volume of the footwear while providing the appropriate support and flexibility to the foot, (2) providing manufacturing efficiencies by reducing the number of components parts, (3) being conducive to facilitating the engineering freedom needed to provide the desired performance characteristics, (4) providing an aesthetically pleasing appearance to the consumer, (5) providing support and performance traditionally only obtainable from a lasted construction, (6) reducing weight and/or bulk while providing the desired support and fit, (7) reducing or eliminating break-in time, (8) extending the longevity of the footwear by minimizing degradation resultant from use, and (9) implementing a non-lasted footwear construction.